Fix overflow in awq kernel (#1295)

Co-authored-by: 楚天翔 <tianxiang.ctx@alibaba-inc.com>

csrc/quantization/awq/gemm_kernels.cu

@@ -90,7 +90,7 @@ __global__ void __launch_bounds__(64) gemm_forward_4bit_cuda_m16n128k32(int G, i
                             + (((int)threadIdx.x) % (128 / 8)) * 8;
 
   half* C_ptr = C 
-              + blockIdx_z * M * OC        // blockIdz.x -> split_k dim
+              + static_cast<long long>(blockIdx_z) * M * OC        // blockIdz.x -> split_k dim
               + (((int)blockIdx_y) % j_factors1) * 128
               + ((int)threadIdx.y) * 64
               + (((int)threadIdx.x) % 4) * 2;
@@ -323,7 +323,7 @@ __global__ void __launch_bounds__(64) gemm_forward_4bit_cuda_m16n64k32(int G, in
                             + (((int)threadIdx.x) % (64 / 8)) * 8;
 
   half* C_ptr = C 
-              + blockIdx_z * M * OC        // blockIdz.x -> split_k dim
+              + static_cast<long long>(blockIdx_z) * M * OC        // blockIdz.x -> split_k dim
               + (((int)blockIdx_y) % j_factors1) * 64
               + ((int)threadIdx.y) * 32
               + (((int)threadIdx.x) % 4) * 2;